Chapter 14: Responses to stimuli

Question 1

stimuli

Answer 1

a change in the internal or external environment that leads to a response

Question 2

taxes

Answer 2

a simple response seen in animals that involves movement away or towards a stimulus

Question 3

kinesis

Answer 3

a simple response to a non-directional stimulus (humidity) in which the organism changes the speed at which it moves and the rate at which it changes direction

Question 4

tropism

Answer 4

a plant growth response to a directional stimulus

Question 5

receptor

Answer 5

detect stimuli

specific to one type of stimuli

e.g. light, pressure, glucose conc.

many different types

can be cells or proteins found on cell-membranes

Question 6

effector

Answer 6

carries out a response

Question 7

coordinator

Answer 7

formulates an appropriate response to a stimuli

Question 8

negative taxes

Answer 8

a form of taxes that involves moving away from an unfavourable stimulus

Question 9

positive taxes

Answer 9

a form of taxes that involves moving towards a favourable stimulus

Question 10

positive tropism

Answer 10

…

Question 11

negative tropism

Answer 11

…

Question 12

phototropism

Answer 12

plant growth in response to light

Question 13

gravitropism

Answer 13

growth in response to gravity

Question 14

Why is it important that animals respond to stimuli?

Answer 14

The ability to respond to stimul

• increases chances of survival
• avoiding harmful environments
• maintain optimal internal enviornments for metabolism

Question 15

reflexes

Answer 15

automatic, rapid responses to stimuli

Question 16

Why are reflexes important?

Answer 16

automatic - don’t have to think/decide - rapid

reduce amount of harm/protect the body

Question 17

relfex arc

Answer 17

the pathway of neurones linking receptors to effectors in a relfex

Question 18

Briefly describe a simple reflex arc

Answer 18

stimulus

heat

receptor

thermoreceptors in skin detect heat

sensory neurone

send impulse from receptor to relay neurone

relay neurone

sends impulse from sensory to motor neurone

motor neurone

sends impulse to effector

effector

bicep muscle contracts to pull arm away

Question 19

When can a reflex be overriden?

Answer 19

If there is a relay neurone in the reflex arc the reflex can be overriden

Question 20

Characteristics of nervous communication.

Answer 20

localised

neurotransmiter are released directly onto target cells

short-lived

neurotransmitters are removed

rapid

electrical impulses travel fast

Question 21

Why is it important for plants to be able to respond to stimuli?

Answer 21

increases their chances of survival

• allows them to grow towards light
• maximum absorption of light for photosynthesis
• roots can grow in the right direction
• climbing plants can find things to climb to reach sunlight

Question 22

Are shoots negatively or positively phototropic?

Answer 22

Shoots are positively phototropic

They grow towards light.

Question 23

Are roots negatively or positively phototropic?

Answer 23

Roots are negatively phototropic

They grow away from light

Question 24

Are shoots negatively or positively gravitropic?

Answer 24

Shoot are negatively gravitropic.

They grow upwards

Question 25

Are roots negatively or positively gravitropic?

Answer 25

Roots are **positively gravitropic** They grow downwards

Question 26

growth factors

Answer 26

**hormone-like** chemicals that **speed up or slow down** plant growth **produced** in the growing parts of a plant (the tips of shoots and leaves) **transported** to where they are neeeded

Question 27

auxin

Answer 27

**type of growth factor** **in the shoots** auxin **stimulates growth** in shoots by **cell elongation** where cell walls become stretched and loose making the cells longer **in the roots** auxin **inhibits** cell elongation and growth **indoleacetic acid (IAA)** is an auxin

Question 28

Indoleacetic acid

Answer 28

an auxin produced in the shoot tips of flowering plants moved around the plant to control tropism over short distances via diffusion and active transport and over long distance via the phloem

Question 29

Briefly describe how phototropism works in the shoot tips of a plant.

Answer 29

1. light comes in from **one direction** 2. one side of the shoot **receives** more light than the other 3. IAA **builds up** on the shaded side 4. this **_uneven distribution_** menas **uneven growth** 5. the **higher concentration** of IAA causes cell elongation on the shaded side 6. the shoot **bends** towards the light

Question 30

Briefly describe how phototropism works in the root tips of a plant.

Answer 30

1. light comes in from **one direction** 2. one side of the root **receives** more light than the other 3. IAA **builds up** on the shaded side 4. this **_uneven distribution_** means **uneven growth** 5. the **higher concentration** of IAA **inhibits** growth 6. the root **bends away** from the light

Question 31

Briefly describe how gravitropism works in the shoots and roots of a plant.

Answer 31

1. **IAA builds** up on the **underside/lowerside** of shoot and roots 2. this **_uneven distribution_** means **uneven growth** 3. the higher conc. of IAA on the underside of shoots causes **cell elongation** 4. so that shoots grow **upwards** 5. the higher conc. of IAA on the underside of roots **inhibits** cell growth 6. so that roots grow **downwards**

Question 32

How does kinesis keep simple organisms in a favourable environment?

Answer 32

kinesis **favourable**: move slowly and don't change direction as often so increases chance of staying in a favourable area **unfavourable**: increase speed and turn more often so increases chance of moving into a favourable area -improving chances of survival e.g. woodlice use kinesis to stay in areas of **high humidity** - **reduces water loss** and helps to **conceal** them

Question 33

Pacinian corpuscle

Answer 33

receptors found deep in the **skin** hands, soles of the feet, external genetalia, ligaments, etc detect **mechanical stimuli** changes in **pressure/**vibrations a single **sensory neurone** or **sensory nerve ending** wrapped in layers of **cell tissue/connective tissue** called **lamellae**

Question 34

photoreceptors

Answer 34

**light receptors** found in the **eye** convert light into an electrical impulse

Question 35

cones

Answer 35

a **type** of photoreceptor found packed in the **fovea** of the retina that give **trichromatic** vision

Question 36

rods cells

Answer 36

a **type** of photoreceptor found in the **peripheral** parts of the retina that give us **monochromatic** vision

Question 37

Briefly decribe what happens when a Pascinian corpuscle is in its resting state and when it is stimulated.

Answer 37

Resting: * resting potential * the stretch-mediated sodium channels are too narrow to let sodium ions to diffuse in * the inside is more negative than the outside Stimulated: * Pressure is applied and the membrane is stretched/deformed * causes stretch-mediated sodium channels to **widen** * sodium ions able to diffuse in * influx of sodium ions causes depolarisation of the membrane * inside becomes more positive than the outside * called the generator potential * the generator potential could lead to an action potential

Question 38

rod cells

Answer 38

low visual acuity retinal convergeance * more numerous than cone cells sensitive * monochromatic vision because different wavelengths cannot be distinguished *

Question 39

retinal convergeance

Answer 39

lots of rod cells are connected to 1 sensory neurone this means that it is more likely that the threshold value will be reached to create a generator potential becase lots of low level depolarisations in the rod cells can accumulate to reach the threshold value

Question 40

What does it mean for rod cells to have low visual acuity?

Question 41

What is the pigment found in rod cells?

Answer 41

Rhodopsin

Question 42

control of heart rate

Answer 42

o